This disclosure is generally related to drive and directional control systems for vehicles, and more particularly to drive and directional control systems and devices for utility vehicles having Mecanum wheels, such as lawn and garden tractors or mowers.
Traditional vehicle maneuverability, such as that of a garden tractor equipped with a hydrostatic transmission and an internal combustion engine, is accomplished by a combination of driven wheels powered by a single transmission, a transmission control, steered wheels, a steering control, and a throttle. The operator of such a vehicle, after startup, first sets the engine speed with the throttle. Next, the operator displaces the transmission control, such as a hand or foot control, to select a forward or reverse direction of travel and also the speed of travel. Simultaneously, the operator steers the vehicle, typically with a steering wheel and mechanical linkage to the steered wheels. This type of vehicle and control may result in limited maneuverability, e.g., a wide turning radius that limits the ability of the vehicle to travel in tight quarters.
In an attempt to improve maneuverability, zero turn vehicles, such as zero turn mowers, were introduced. One type of zero turn vehicle uses independently controlled transaxles to provide steering by selectively speeding up, slowing down, or changing the direction of rotation of the driven wheels on each side of the vehicle. Typically, an operator has a pair of levers that independently control the speed and rotational direction of the output of a transaxle on each side of the vehicle, and thus the speed and rotational direction of the associated driven wheel. If an operator wishes to move the vehicle forward, he presses both levers forward. If the operator wishes to move the vehicle backwards, he pulls both levers back. To steer the vehicle to the left, the right side lever is pushed further than the left, and to execute a very tight turn to the left, the operator can pull the left lever back while pressing the right lever forward to execute a zero radius, or near zero radius turn. Traditionally, zero turn mowers do not have steered wheels per se, but rather a pair of caster wheels at the front of the vehicle which respond to the actions of the driven rear wheels. Zero turn mowers with steering wheels are also available, but they generally have complex mechanical linkages to coordinate the movements of a pair of steered front wheels with the outputs of the driven rear wheels.
An alternate steering input device, such as a joystick and associated controller, may be used to control the outputs of the independent transmissions of a zero turn vehicle. Comparatively speaking, the steering wheel system is easy to operate but may lack the maneuverability and programming flexibility of a joystick control system, and the lever activated differential steering systems may simply be more difficult to use for some vehicle operators.
The wheels on vehicles may include various types of tires, casters, and the like. One particular type of wheel is a Mecanum wheel that has a series of angled rollers attached to the outer circumference of the wheel. Vehicles equipped with Mecanum wheels are omnidirectional in that they can move in any direction by varying the speed and direction of rotation of each of the Mecanum wheels in a coordinated manner. For example, a vehicle with Mecanum wheels can move forward or backward by driving its wheels in the same direction, can rotate in place (zero turn) by driving the wheels on one side of the vehicle in the opposite direction as the wheels on the other side of the vehicle, and can additionally move sideways by driving the wheels on one diagonal of the vehicle in the opposite direction as the wheels on the other diagonal. This disclosure is directed to addressing the problems and needs of drive and steering systems related to highly maneuverable utility vehicles having Mecanum wheels.